Even after 6 months, typical compensation for being fired is 2 weeks of salary for every year worked. For most startup employees, this won't be a huge amount, given they have often only worked a few years.

Doesnt that make my point ? You can easily be fired in a probation period :-) and right before the probation ends is when the employer wonders if they should keep you (really hire you for good)

In theory, this is true. However, IME as a techie in the UK, those situations happen when there is a significant mismatch between the interview vs reality - from either side. Hiring based on referrals is one way to mitigate some of the unknowns.

After 5 months of being embedded in a team, firing someone who management doesn't like but who is popular with other employees will cause major morale issues even if they are still technically in probation.